实体框架：调用保存更改时出错

Question

I am working with entity framework to connect MySql. I have created a entity data modal with the MySql database, it generate the connection string in web.config automatically which is as follows in my case:-

 <add name="entityframework1" connectionString="metadata=res://*/EntityFramework.csdl|res://*/EntityFramework.ssdl|res://*/EntityFramework.msl;provider=MySql.Data.MySqlClient;provider connection string=&quot;server=localhost;User Id=root;database=entityframework&quot;" providerName="System.Data.EntityClient" />

Now I want to save record in database and the code is as follows:-

        employee emp = new employee();
        emp.Name = txtName.Text;
        emp.Age = Convert.ToInt32(txtAge.Text);

        using (entityframework context =
              new entityframework())
        {

            context.AddToemployees(emp);
            if (context.SaveChanges() == 1)
            {
                lblMsg.Text = "Saved Successfully.";
            }
        }

it gives error

"object reference not set to an instance of object" on the if condition having "context.SaveChanges".

I also tried to pass the connection string at the time of creating context

string connectionstring = "SERVER=localhost;DATABASE= entityframework ;UID= root;";

but it gives error that "Keyword not supported: '"server'." this is my first effort in entity framework, is there anybody to advise me.

Answer 1

If you can retrieve data from the server then the connection string is good.

As for the SaveChanges() try calling context.ChangeTracker.DetectChanges() first and as a success condition you can set the initial id of the entity to -1 for instance and afterwards check if it is >= 0. (That is, if your PrimaryKey is also Autoincrement/Identity)

Answer 2

You need to also add the following to your web.config file (replace the Version string with the appropriate version of your MySQL .NET connector)

<system.data><DbProviderFactories>
  <clear />
  <add name="MySQL Data Provider" invariant="MySql.Data.MySqlClient" description=".Net Framework Data Provider for MySQL" type="MySql.Data.MySqlClient.MySqlClientFactory, MySql.Data, Version=6.6.5.0, Culture=neutral, PublicKeyToken=c5687fc88969c44d" />
</DbProviderFactories></system.data>